This is general question, and one that I realize the answers to may vary, depending on several issues (amp size, use, etc.)
I have two amps (taken out of my old car) that I plan to use in a new install, in a 1998 Pontiac Sunfire. Both are comparatively small. One is an old (but still useful) Crutchfield model 187CR "Performance" series 2x30 rms, the other is a Sony model XM2540 4x25RMS. Both are decent MOFSET items which can be bridged to deliver 1x60 and 2x50 if required.
The Sunfire is not a huge car, and I'm in the typical situation of searching for places to put the amps (this install is designed to sound good, not compete or impress people with fancy trunk setups, flashing lights, etc.) Frankly, I'm trying to do the install to keep the car looking as EOM as possible, ergo trying to avoid using trunk space to the degree possible for the amps.
I've discovered that the Crutchfield amp (which isn't big, about 6.5" wide, 1.5" tall and 9" deep) could fit into a small space up front, under the middle of the dash down near the floor (inbetween the kick panels in front of the console). The issue is, if the amp is put there, it's going to sit jammed into a tight space borderd by ventilation system runs.
I know from experience in my last car (where the amp sat under the drivers seat, that won't work in the Sunfire, not enough space) that it barely gets warm (probably because I don't blast away with my music).
So, part of me is thinking "heck, I know amps are supposed to have a few inches of venilation space, but this thing doesn't get hot, so it will be fine in that little space up front, especially if I put a little fan in above it", while another part of me is thinking "yeah, but rules are rules." Any thoughts? If it helps, the amp would be used to drive a pair of front speakers, Infinity Reference 4x6 plates that are rated for up to 50 watts RMS.
As for the Sony, it's only a little larger than to the Crutchfield, but still too big to go anywhere I've found under the dash, or under the seats, so I'll probably tuck it into a back corner of the trunk (where it won't be noticed unless someone is really leaning over to look; I've also considered a shelf under the rear deck, but given the design of the Sunfire that is a less desirebale option given it cuts down on a surprising amount of usable trunk space). Yes, I know the Crutchfield could fit there too, but again, I'd prefer to put as little as possible in the trunk.
mikeymars